Infrared technology has a wide variety of applications, ranging from missile defense to meteorology and medical diagnostics. Two important applications are guidance systems and reconnaissance devices.
An essential part of every infrared system is the radiation detector. Known types of detectors are photodetectors, pyroelectric detectors and thermal detectors or bolometers. When photodetectors operate at wavelengths beyond three microns, they must be cooled by liquid helium or liquid nitrogen devices which occupy space and consume power. Pyroelectric detectors which are fabricated from ferroelectric materials whose dielectric polarization responds to a change in temperature and bolometers which are made from materials whose conductivity is temperature sensitive, do not require such cooling. Rather, they respond to long-wavelength radiation at ambient operating temperatures. Thus, they have found wide use in applications in which a flat, extensive, spectral response is required or where little weight can be allowed for bulky cryogenics.
Owing to the fact that pyroelectric detectors and bolometers are severely noise limited by the properties of the materials of which they are made, they suffer from poor responsivities. As a result, it is difficult to build such devices into high resolution imaging systems.